(1) Field of the Invention
The present invention relates to a pencil head used for pencil-drawing in an automatic drawing instrument, particularly, to a pencil guide thereof used for guiding an up-and-down motion of a pencil.
(2) Description of the Prior Art
A typical example of a conventional pencil head used for a pencil drawing device mounted on an automatic drawing instrument is shown in FIG. 1. In this exemplified conventional pencil head, 1 denotes a holding turret for pencils, 2 denotes a gear, and 3 denotes a pinion, which is driven by a driving device (not shown) so as to enable the rotation of the holding turret 1 by rotating the gear 2 therewith. 4 denotes a pair of bearings, and 5 denotes one of a number of tubular members held in the holding turret 1 for guiding pencils therethrough respectively. The up-and-down motion of the tubular member 5 required for the pencil-drawing is effected by a spring 6 provided for raising it and a lowering mechanism consisting of a solenoid 7, an arm 8, a pin 9 and a spring 10 for lowering it.
For tightening the holding turret 1, an inserting hole 12a for inserting a pin 12 supported by a fixed bracket 14 is provided in a connecting member 11 which forms an upper part of the holding turret 1, and further another inserting hole 13a is provided in the connecting member 11 at right angles to the inserting hold 12a for inserting a cotter 13, which can be slid through a bearing metal 15 buried in the fixed bracket 14 and pushed forward by a spring 16, so as to pull up the connecting member 11 for tightening the holding turret 1. On the other hand, the release of the holding turret 1 from the pencil drawing device can be effected by drawing out the cotter 13 from the further pulled up connecting member 11.
18 denotes a pencil lead pushing stick employed as a medium for generating the pencil lead pressure, an upper end thereof being supported by clamps 20, 21 and a spring 22, which are provided on a bracket 19. 23 denotes a rack provided in parallel with the pencil lead pushing stick 18, an upper end thereof also being supported by the bracket 19. 24 and 25 denote a guide and a bearing metal respectively, which are fitted on a lower end of the rack 23. 26 denotes a pinion engaged with the rack 23. 27 denotes a motor accompanied with a detector and coupled with the pinion 26, by driving which motor 27 the rack 23 is lowered so as to apply the pencil lead pushing stick 18 with the pushing force required for causing the pencil lead pressure.
The above-mentioned conventional pencil head is arranged for moving the tubular member 5 up and down, so that the most external shape of the tubular member 5 is enlarged and the weight thereof is increased, and further the external shape of the upper part of the holding turret 1 is enlarged and the weight thereof is increased also. Moreover, the solenoid 7 and the motor provided for causing the pencil lead pressure co-operate with the timing matched with each other for moving the tubular member 5 up and down, so that the speed of the up-and-down motion is lowered and, as a result, the high speed drawing cannot be expected. Besides, the operation for mounting and releasing the holding turret 1 is troublesome and the mechanism therefor is complicated, and further the space between the holding turret 1 and the drawing surface 17 is apt to be varied, and, as a result thereof, the shift of drawn pictures and the break of the pencil lead accompanied with a long residual lead are caused easily during the drawing. Consequently, the conventional pencil head shown in FIG. 1 has such various kinds of defects as mentioned above.
On the other hand, another typical conventional pencil head employed for the pencil drawing device mounted on the automatic drawing instrument is arranged as shown in FIG. 2. In FIG. 2, 71 denotes a holding turret for holding pencil leads 72. 73 denotes a resilient member formed, for example, of rubber, 74 denotes a pencil lead guide, 75 denotes a tubular member, 76 denotes a spring and 77 denotes an enlarged portion of the tubular member 75. A number of holes (not shown) in which pencil lead guides 74 and tubular members 75 should be inserted individually are formed on the peripheral portion of the holding turret 71. FIG. 2 is a cross section showing one of those holes in which one the pencil lead guide 74 containing the resilient member 73 provided for holding the pencil lead 72 and the tubular member 75 connected to the pencil lead guide 74 are inserted, and further the spring 76 is fitted on the lower face of the enlarged portion 77 of the tubular member 75 as shown in FIG. 2. The up-and-down motion of the pencil guide during the drawing is effected by moving up and down the pencil lead 72, the resilient member 73 and the pencil lead guide 75 on the strength of the spring 76 and a pencil guide lowering device (not shown) which is provided externally.
In the above-mentioned arrangement, it is required for moving the tubular member 75 up and down smoothly that the tubular member is formed of a material having such a sufficient stiffness as bearable against an oscillating force generated by the up-and-down motion of the tubular member 75, and further the enlarged portion 77 of the tubular member 75 is indispensable for fitting the spring 76 on the periphery thereof. Accordingly, the most external shape of the pencil guide is inevitably enlarged as well as that of the holding turret 71 holding a number of those enlarged pencil guides on the peripheral portion thereof is enlarged also, and further the weight of the pencil guide cannot be reduced and the structure thereof is extremely complicated. Furthermore, the renewal at least of the resilient member 73, the pencil lead guide 74 and the tubular member 75 is necessitated by the defacement and the damage thereof caused by the secular change of the resilient member 73.
In addition thereto, in the conventional pencil-drawing device shown in FIG. 2, as mentioned earlier, the up-and-down motion of the pencil lead 72 during the drawing is effected by the pencil lead guide 74 containing the resilient member 73 which holds the pencil lead 72, the spring 76 provided for raising the pencil lead guide 74, the lowering device (not shown) provided with an arm 78 lowering the pencil lead guide 74 and a pencil-pressure device (not shown) provided with the pencil lead pushing stick 79 causing the pencil-pressure.
The up-and-down moving mechanism for pencil which is arranged as mentioned above has such a defect as the weight thereof is increased by a large number of parts thereof, so that the speed of the up-and-down motion of the pencil lead 72 and accordingly that of the drawing cannot be increased. Furthermore, for lowering the pencil lead during the drawing, the one-body member consisting of the resilient member 73 holding the pencil lead 72, the pencil lead guide 74 and the tubular member 75 is slid down through the hole formed on the peripheral portion of the holding turret 71 on the strength of the arm 78, and then the pencil lead 72 is pushed by the pencil lead pushing stick 79 so as to generate the pencil pressure. On the other hand, for raising the pencil lead during the drawing, the pencil lead pushing stick 79 is raised by the release of the arm 78, and then the one-body member consisting of the resilient member 73, the pencil lead guide 74 and the tubular member 75 is raised on the strength of the spring 76. Consequently, the up-and-down motion of the pencil lead 72 during the drawing is effected by the co-operation of the arm 78 and the pencil lead pushing stick 79 which is provided with a certain fixed time spacing between each other, so that the high fidelity and the quick response of the up-and-down motion of the pencil lead 72 and the shortening of the time duration required for the drawing cannot be realized.